When there is a single asset or resource, such as a personal computer data bus, that needs to be used by a plurality of requesters, such as a modem, a hard disk and/or a software program, some kind of allocation scheme needs to be provided. If no one is in an extreme hurry, a round robin scheme has been used in the past where, on a given clock cycle, one device request line is polled to ascertain whether or not that requester or device has a need for the asset and if there is a request, the request is granted for an indeterminate time. After that request is removed or finished, the system proceeds to the next requester in line. If someone far down the line of requesters in the round robin circuit has a request even though no one else has a request between the present arbitration logic circuit and the one connected to a requester requiring access to the asset, it still in the prior art, has required a number of clock signals equal to the number of intermediate requesters to get to the requester having a present need to acquire the use of the asset.
For this reason, most present-day schemes for determining who gets access to an asset, use a priority interrupt scheme where the requester with the most priority, is always the next one to have access to the asset. Unfortunately, with such a scheme, a requester with low priority sometimes needs to wait an extremely long time before being granted access to an asset.
The present scheme uses a round robin approach to assure everyone equal access opportunity but provides for a substantial decrease in time to perform the round robin cycle times by providing a plurality of different phase clock signals for each of N arbitration circuits so that the round robin cycle for N arbitration circuits can be completed in less than N clock duration times. With the proper circuitry, the entire round robin cycle can be completed within one clock duration time period if there are no active requests.
The scheme referenced above can be easily modified to provide for giving at least one of the requesters a priority interrupt for interrupting any other requester's use of an asset and then allowing the system to return to the round robin scheme after the priority requester has completed his use of the asset.
It is therefore an object of the present invention to provide an improved arbitration circuit using a round robin approach with phase delayed clock signals to improve the access time of the round robin scheme.